002 025 ch01 re 896315.qxd 3/31/10 2:09 pm page 2 s-034 ...€¦ · 2 chapter 1 the nature of...

What You’ll Learn

■ how scientists solveproblems

■ why scientists use variables

■ how to compare andcontrast science lawsand theory

When you hear the word scientist, what comes to mind?Brainstorm some words that describe a scientist. Write themon the lines below.

What is science?Science is not just a subject in school. Science is a way of

studying the world. The word science comes from a Latinword that means “knowledge.” Science is a way to learn orgain knowledge by observing and investigating.

Nature follows a set of rules. The rules for understandinghow the human body works are complicated. The rules forunderstanding the pattern of Earth spinning once every 24 hon its axis are simpler. Scientists ask questions to learn aboutthe natural world.

What are the major categories of science?Science covers many different topics. These topics fall

under three main categories: life science, Earth science, andphysical science. Life science is the study of living things.Earth science is the study of Earth and space. Physical scienceis the study of matter and energy. In this book, you will studymainly physical science. You also will learn how these threemain categories sometimes overlap.

How does science explain nature?Scientific explanations help explain the natural world.

Scientists investigate and use technology to get new information.Sometimes, this new information causes scientific explanationsto change. In the 1700s, most scientists thought heat was a fluid.After many studies, they concluded heat is not a fluid.

Before You Read

Read to Learn

2 CHAPTER 1 The Nature of Science

●A Build VocabularyMake the following Foldable tohelp you learn key terms fromthis section. You will need tomake more than one Foldable.

chapter The Nature of Science

section ● The Methods of Science

1

Identify Highlight each heading that is a question. Use a different color of marker tohighlight the answers to thequestions.

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Variable

Dependent Variable

IndependentVariable

Constant

Control

ScientificMethod

Hypothesis

Experiment

1

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Reading Essentials 3

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2. Interpret Why are theretwo arrows leading todifferent parts of the chart at the bottom?

Picture This

1. Draw Conclusions Whymight steps in scientificmethods be skipped orchanged?

Scientific MethodsA scientific method is a set of steps used in an investigation.

Scientists follow steps similiar to those listed below whendoing an investigation. These steps guide the scientist. Somesteps may be repeated. Other steps may be skipped. The flowchart below shows six common steps found in variousscientific methods.

“What material can be used to cover the space shuttle to keep it from burning up during

re-entry into Earth’s atmosphere?”

Do research on melting points and other properties of various materials including

newly created materials.

Hypothesis: A certain ceramic material could be used to make a protective

covering for the space shuttle.

Build two identical model shuttles. Cover one with the ceramic material and the other with a

different material. Expose both models to strong blasts of super-heated air.

The model with the special ceramic coating withstood the strong blasts of

super-heated air better.

A certain ceramic material seems to protect the model space shuttle

better than other materials.

Test other ceramic materials (Restate the problem; reviewgathered information; check data

collected; modify hypothesis.)to see which one protects the

model space shuttle best.

State the problem

Gather information

Form a hypothesis

Test the hypothesis

Analyze data

Draw conclusions

Hypothesis supportedHypothesis not supported

RepeatSeveralTimes

ModifyHypothesis


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Stating a Problem Many scientific investigations begin witha question about how or why something happens in nature.The problem is stated as a “how” or “why” question.Sometimes a question is asked because scientists want toimprove upon something. Early work on guided missilesshowed that the nose cone instruments needed a material toprotect them from heat. Later, National Aeronautic andSpace Administration (NASA) scientists wanted to find amaterial to protect the space shuttle from the heat andforces of re-entry into Earth’s atmosphere.

Researching and Gathering Information It is important to study a problem before any testing is done. Sometimessomeone has already solved a similar problem. NASA scientists gathered information about melting points andother properties of various materials that might be used.They also performed tests on newly created materials.

Forming a Hypothesis A hypothesis is a possibleexplanation for a question or problem based on what youknow and what you observe. A scientist who forms ahypothesis must be certain it can be tested. NASA scientistsknew that a certain ceramic material had been used to protectthe nose cones of guided missiles. They hypothesized that aceramic material might also protect the space shuttle.

Testing a Hypothesis Some hypotheses are simply testedby making observations. Building a model may be the bestway to test a hypothesis. Scientists may also use an experimentto test a hypothesis. The experiment looks at how one thingaffects another under controlled conditions. NASA scientistsbuilt model space shuttles and covered them with variousmaterials. They tested the models in simulated re-entryenvironments to see which material gave the best protection.

Variable An experiment usually has at least two variables. Avariable is a factor that can cause a change in the results ofan experiment. Suppose you set up an experiment to seewhich fertilizer makes plants grow biggest. First, you need tothink of all the factors that can make a plant grow bigger.These might include the type of plant, amount of sunlight,amount of water, type of soil, and amount of fertilizer.

In this experiment, the amount of growth is one variable. Itis a dependent variable because its value changes accordingto the changes in other variables. The other variable is theamount of fertilizer. The independent variable is changed tosee how it affects the dependent variable.


3. Research List two places where you mightfind information on the development of the space shuttle.

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4. Define What are the twokinds of variables that aretested in experiments?


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Constants and Controls To keep an investigation fair, allother factors must be the same. A constant is a factor in anexperiment that does not change. In the fertilizer experiment,the constants are the amount of water and sunlight the plantsget and the temperature at which the plants are kept. Theseare the same for all plants tested. Three plants get differentamounts of fertilizer, which is the independent variable.

A control is used to compare the results of the experiment.One plant is a control and does not get any fertilizer, but doesget the same sunlight, water, and temperature as the otherplants. Suppose after several days that the control plants growbetween 2 and 3 cm. If the unfertilized plant grows only 1.5cm, you might infer that the greater growth of the fertilizedplants was caused by the fertilizer.

Analyze the Data An important part of any experiment isrecording observations and organizing information. Allresults and observations should be recorded during anexperiment. Many important discoveries have been madefrom unexpected results. The information or data should beorganized into an easy-to-read table or graph. Later in thischapter, you will learn how to show your data.

Understanding what the data and observations mean is also important. The data must be organized logically. Poorlyorganized data may lead to a wrong conclusion. Scientistsshare their data through reports and meetings. Scientists maydisagree about certain data, no matter how well the data ispresented.

Drawing Conclusions Scientists look at their data and decideif the data support the hypothesis. If the data is the sameafter many experiments, the hypothesis is supported. If thehypothesis isn’t supported, scientists may change it or theexperiment.

Sometimes others don’t agree with the conclusions, so theydesign new experiments to test the hypothesis. In time, datawill support a valid hypothesis.

Being Objective Scientists must avoid a bias. A bias occursin an experiment when a scientist expects something tohappen and lets this influence how the results are viewed.Scientists try to reduce bias whenever they can by doing the experiment many times and keeping careful notes about observations. Also, other scientists repeat the sameexperiment to see if they get the same results.

6. List two reasons why datamust be organized.

5. Classify Is the plant thatreceives no fertilizer in theplant experiment a variable,a constant, or a control?


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Visualizing with ModelsSometimes, scientists cannot see everything they are testing.

They might be studying something too large or too small tosee. It might even take too much time to see completely. Inthese cases, scientists use models. A model represents an idea,event, or object to help people better understand it. A modelmay be a physical object such as a scaled-down version of thespace shuttle. A model can also be represented by a drawingon paper or by a computer program.

Models in History Models have been used throughout history. Lord Kelvin, a scientist who lived in England in the1800s, was famous for making models. To model his idea ofhow light moves through space, he put balls in a bowl ofjelly. He asked people to move the balls with their hands.Kelvin’s work explaining heat and temperature is still usedtoday.

What are high-tech models?Scientific models don’t have to be something you can touch.

Many scientists use computers to build models. Computermodels are used to solve difficult mathematical equations.NASA uses computers in experiments with space flights tosolve equations that are too hard or would take too long tosolve by hand.

Another type of model is a simulator. A simulator can create the conditions found in real life. For example, a flightsimulator is a model of an airplane. It can help a pilot pretendto be flying a plane. The pilot can test different ways to solveproblems. The simulator reacts the same way a real plane doeswhen it flies, but there is no danger to either the pilot or a plane.

Scientific Theories and LawsA scientific theory is a way of explaining things or events

based on what has been learned from many observations andinvestigations. When these observations and investigationshave been repeated many times and support the hypothesis,then the hypothesis becomes a theory. New information inthe future may change the theory.

7. Explain What are models?

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8. List three differencesbetween a flight simulatorand a real airplane.


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A scientific law is a statement about what happens innature and seems to be true all the time. A law explains whatwill happen under certain conditions, but it does not explainwhy or how it happens. Theories are used to explain how andwhy laws work. Gravity is an example of a scientific law. Thelaw of gravity says that any one mass will attract anothermass. To date, no experiments have been done that prove thislaw is not true.

The Limitations of ScienceScience is used to explain many things about the world.

However, science cannot explain everything. Questions aboutemotions or values are not questions science can answer. Asurvey of peoples’ opinions would not prove that theseopinions are true for everyone. Scientists make predictionswhen they perform experiments. Then these predictions aretested and verified by using a scientific method.

Using Science—TechnologyThe words science and technology often are used in place of

each other. However, the two words mean different things.Technology is the application of science to help people. Forexample, science methods are used when a chemist develops anew material. When this new material is used on the spaceshuttle, technology is applied.

Sometimes technology comes before science. For example,when the steam engine was invented, no one knew exactlyhow it worked. Scientists studied it and learned about thesteam engine. This led them to discover new ideas about thenature of heat.

Not all technology produces something good. Some peoplequestion the benefits of some technology, such as nucleartechnology. Learning more about science can help societymake decisions about these issues.

10. Think Critically Give anexample of whentechnology is anapplication of science.

9. Restate What is a scientific law?

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1. Review the terms and their definitions in the Mini Glossary. Write a sentence explaininghow bias can influence an experiment.

2. Complete the chart below to organize the information you have learned in this section.Put the following steps for scientific methods in order.

Analyze the data, Test the hypothesis, State the problem, Draw conclusions, Gather information,

Form a hypothesis

bias: what is expected changes how the results are viewed

constant: a condition in an experiment that does not change

control: a standard in an experiment against which the results

are compared

dependent variable: the condition in an experiment

that results from the changes made to the independent

variable

experiment: an investigation that tests a hypothesis by

collecting information under controlled conditions

hypothesis: an explanation for a question or a problem that

can be tested

independent variable: in an experiment, the condition

that is tested

model: anything that represents an idea, event, or object to

improve understanding

scientific law: a statement about what happens in nature

that seems true all the time

scientific method: the steps a scientist follows when

performing an investigation

theory: an explanation that is supported by a large body of

scientific evidence obtained from many different

investigations and observations

variable: a quantity that can have more than a single value

After You ReadMini Glossary

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Think about graphs that you have seen. Why do you thinkgraphs are a useful way to display information?

What You’ll Learn

■ identify three types ofgraphs and tell howthey are used

■ how to distinguishbetween dependentand independentvariables

Before You Read

Read to LearnA Visual Display

A graph is a visual display of information or data. Oftengraphs are used to show results of experiments. Patterns indata show better in a graph than when data are in a table.The most common types of graphs are line graphs, bargraphs, and circle graphs. Each type of graph is used to showdifferent types of data. Graphs make data easy to compare.

Line GraphsLine graphs show how a relationship between variables

changes over time. A line graph can show more than oneevent on the same graph. For example, a builder had a choiceof three brands of thermostats to install in school classrooms.He tested each brand to find the most efficient one. Thebuilder set each thermostat at 20°C. He checked the classroomtemperature every five minutes for 25 minutes and recordedthe data.

The graph on the next page shows the results of the test.The break in the vertical axis between 0 and 15 means thatthe numbers 1 to 14 have been left out. This is done so thereis more room to spread the scale and the graph is easier toread. The horizontal line represents the 20°C setting and isthe control in this experiment. The three lines (A, B, and C)show how quickly each thermostat reached the setting of 20°C.

Identify the Main PointAs you read through this section, highlight two mainpoints about a line graph, a bar graph, and a circle graph.

●C Compare andContrast Make the followingFoldable. Use each section todraw an example of one type ofgraph.


section ● Communicating with Graphs

13

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LineGraphs

BarGraphs

CircleGraphs

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How do you construct line graphs?There are several steps that you must follow to make a

line graph. Always use the horizontal axis, or x-axis, for the independent variable. The vertical axis, or y-axis, is alwaysused for the dependent variable. You should select a scale thatmakes your graph sensible and readable. For example, thescale on the x-axis would not make sense or be very readable if the units were by hours instead of minutes. All of lines A, B,and C that you see on this graph would be in the first tenth ofthe section ending with 5.

The data on a line graph are related. To draw the lines, youfirst plot points that show the relationship of the variables. Forexample, in line B, after five minutes the temperature was17°C. You plot a point that aligns with 5 on the x-axis and 17on the y-axis. Then plot the points representing the other data.Then you draw a line to connect the points.

You must also make sure that all the data use the sameunits. If some measurements were made in the Celsius scaleand others were made in the Fahrenheit scale, the units mustbe converted to the same unit of measurement.

Bar GraphsBar graphs are useful for comparing data collected by

counting. Each bar shows a number counted at a particulartime. As on a line graph, the independent variable is plottedon the x-axis, and the dependent variable is plotted on the y-axis. The data are not related so the bars do not touch.

Classroom Temperature

0 5

A

B

C

10 15 2520

Tem

pera

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(�C)

0

15

16

17

18

19

20

21

22

23

24

25

26

Time (min)

2. Describe What kind of dataare bar graphs useful for?

1. Interpret Which thermostat reached its temperature setting thequickest?

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Example The bar graph below shows classroom size on oneday (January 20, 2004). The height of each bar shows thenumber of classrooms having a particular number of students.For example, three classrooms had 21 students. The numberof students in one classroom is not related to the number ofstudents in other classrooms. This is why the bars do nottouch.

Circle GraphsA circle graph, or pie graph, is used to show how a certain

quantity is divided into parts. The circle represents the wholeand the segments, or slices, are the parts of the whole. Thesegments are usually given as percentages of the whole.

This circle graph below shows how much of each differentkind of heating fuel is used in different buildings. According tothe circle graph, gas is the heating fuel used the most.

When you use a graph, make sure that the conclusions arebased on accurate information. Also select scales that help makethe graph easy to read. In a circle graph, label the sections. Inbar and line graphs, always label both the x-axis and the y-axis.

Classroom Size (January 20, 2004)

Number of students

Num

ber o

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27262524232221200

1

2

3

4

5

6

Gas

50%

Steam

25%

Other

5%

Coal

10%

Electric

10%

Heating Fuel Usage

4. Use Models What do thepercentages in a circlegraph add up to? Why isthis important?

Applying Math

3. Interpret Data How manyclassrooms had 26 students?

Applying Math

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1. Review the term graph and its definition in the Mini Glossary. Write a sentence that tellshow a graph helps you understand data.

2. Complete the outline below. Tell what type of data each type of graph displays and thendraw a small sample of each type of graph.

Three Types of GraphsI. Line Graph

A. data type:

B. example:

II. Bar Graph

A. data type:

B. example:

III. Circle Graph

A. data type:

B. example:

3. Think about what you have learned. Give an example of each type of databest suited for each type of graph.

Line Graph:

Bar Graph:

Circle Graph:

graph: a visual display of information or data


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You use different kinds of technology every day. What do youthink of when you hear the word technology ?

What You’ll Learn

■ types of technology■ value of technology■ consumer effect on

technology

Before You Read

Read to LearnWhat is technology?

The terms science and technology mean very differentthings. Science is a process of exploration. Scientific processesare used to gain knowledge of and predict events in the natural world. Scientists often search for answers to humanneeds and problems. Scientists also search for scientificknowledge for the sake of learning new information.

Technology When scientific knowledge is used to solve ahuman need or problem, the result is called technology.Technology is the use of scientific knowledge of materialsand processes to benefit people. An aspirin pill, a car, and anational highway system may not seem to have much in common. These things are all very different, but they are allexamples of technology. Technology can be:

• any human-made object (such as a radio, computer orhammer),

• methods or techniques for making any object or tool (suchas the method for making glass),

• skills needed to operate a human-made object (such as theskills needed to drive a car), or

• a system of people and objects used to do a task (such asthe Internet, which is a system to share information).


section ● Science and Technology

1

4

●D Classify Make a two-tabFoldable like the one below.Take notes on how differentforces shape technology.

Technology Society

1. Define What is technology?


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What are technological methods or techniques?Just as writing instruments have changed over time, so have

methods or techniques for doing many tasks. The methodsfor printing books have changed over time. Long ago peoplehad to copy each page of a book by hand. This took manyhours. Books were expensive, and only the very rich could payfor them. Now, books are created in many ways. Modernprinting presses create most of the books today. Printing press technology printed your textbook. Books can be writtenon computers and are sometimes printed on computer printers.The printing press and computer technology save countlesshours in producing books.

What are technological knowledge and skills?Technology is not just new machines and new techniques.

It is also the knowledge and the skills needed to do a task. Forexample, you need knowledge and special skills to use mostcomputers. Any skill used to operate a complex machine is atechnological skill.

What are technological systems?A network of people and objects working together to do a

job also is technology. The network is technology, the objectsare technology, and the skills of the people are technology.

The Internet is a good example of this kind of technology.The Internet is a collection of computers and software thatpeople with skills use to send and receive information. Theairline industry is another example of a technological system.This industry is a collection of objects, methods, systems,and rules. An airport’s planes, pilots, and computers create a technology system that moves people and goods.

Global Technological NeedsYou just read how technology has changed over time.

Today, not all parts of the world value the same technologies.The technology valued in the United States may not be valuedin other parts of the world. Industrialized nations have different technology needs than developing nations.

2. Infer What is a technological system that you use each day?

3. Apply Name two technologies that people indeveloping nations couldbenefit from.

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What are the needs of developing countries? In some parts of the world, people work hard for basic

needs such as food, shelter, clean water, and basic health care.Consider a family living in rural Kenya. Most rural Kenyanfamilies live without electricity or running water in theirhomes. Droughts or small amounts of rain can cause foodshortages and famine. Rural Kenyans also have limited healthcare. Because of limited health care infections and diseases,such as HIV/AIDS, are severe problems in many developingnations. The life expectancy of rural Kenyans is mid-forties.

The most important technologies in developing countrieshelp take care of basic needs. Technologies that provideenough clean water and food are very important. Basic healthcare technology such as clean bandages, the right medicine,and skilled doctors are also valued. Generally, rural peoplevalue different technologies than urban people because citiesare more industrialized.

What technology is used in industrialized countries?

The United States is an industrialized country. Because oftechnology, industrialized countries have access to safe, cleanwater and food supplies. Most homes have running water andelectricity. Good health care is available to treat people. Thelife expectancy of Americans is the late-seventies.

People in industrialized nations often value technology thathelps provide a higher quality of life. Most homes in theUnited States have computers, telephones, and televisions.The people of industrialized nations value technologies likefaster computers, compact discs, and safer cars.

Advances in medicine improve people’s lives by curing illnesses and diseases. Some people spend money on medicalprocedures to improve their quality of life. Plastic surgery canremove wrinkles from a person’s face. Eye surgery can improvea person’s vision so he or she may not have to wear glasses.

How do developing nations contrast?Both developing and industrialized nations value

technology that helps supply basic human needs: clean water,enough food, and basic health care. However, the technologyfor basic needs may be very different in developing nations.For example, people in rural areas in some countries couldget clean water if hand-pumps were installed in villages.

4. Explain What are two technologies that are valued in industrializednations?


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Social Forces that Shape TechnologyScience and society are closely connected. Society is a

group of people that shares similar values and beliefs.Discoveries in science and technology change society, andlikewise society affects how new technologies develop. Thepolitics, values, and economics of a society affect what newtechnologies develop.

How did attitudes toward cars change?An example of the connection between a society’s values

and its technology is the development of the car in the UnitedStates. Over the last 100 years, the people of the United Stateshave changed their attitudes toward cars.

When they were first invented, cars were expensive. Thentechnology was developed to mass-produce affordable cars.Many people were able to own cars because of the changes intechnology and manufacturing. This increased the demandfor fossil fuels like gasoline. Technology developed that madegas and oil more accessible and affordable. As more cars weresold, the demand for gas and oil increased.

Now gas prices are high and oil is becoming scarce, so people are beginning to buy more fuel-efficient cars. Theautomobile industry is responding with new technology,such as hybrid cars that use both electricity and gasoline.

Do consumers affect technology?If people do not want a technology, they will not buy it.

Companies are not likely to spend additional money todevelop technology that consumers will not buy. On the otherhand, if consumers buy a technology, companies will spendadditional money to improve the technology. For example, ifconsumers continue to buy fuel-efficient cars, more moneywill be spent on improving that technology.

Do personal values affect technology?People support new technologies that agree with their

personal needs and values, directly and indirectly. For example, people support the development of technology indirectly when they choose to vote for a political candidate.Support for a candidate translates into support for the projects, technological and otherwise, that that candidatefavors. People support the development of technology directlywhen they give money to organizations committed to a specific project, such as cancer research.

5. Explain How does buying a certain brand of CD player affect the development ofCD players in general?


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Economic Forces that Shape TechnologyMany factors influence whether money is spent on a

technology, and many questions must be answered before the money is spent. The questions include who will buy theproduct, what the benefits of the technology are, and howmuch it will cost to make.

What is the influence of the federal government?One way technology research and development is funded is

through the federal government. Every year, Congress and thepresident place large amounts of money in the federal budgetfor scientific research and development. For example,Congress and the president decide how much money will bespent on new technologies in agriculture, defense, energy, andtransportation. The money is given to companies and institutions in the forms of contracts and grants.

What is the influence of private foundations? Some scientific and technological research is supported

with money from private foundations. Foundations raisemoney for many types of research, such as cancer and muscular dystrophy. Foundations raise money in many ways,including charity races, telethons, and benefit concerts. Manyprivate foundations focus on research for specific scientificissues, such as treatment for Alzheimer’s disease.

What is the influence of private industries?Private industries also fund research and development of

new technology. Like the federal government, private industriesuse a portion of their budget on research and development.Investing in new technology can make money for the company.Selling the new products or technologies they develop to consumers is one way companies make profits.

Responsible TechnologyHumans can invent technology that may have an impact on

other living things. Humans are part of many ecosystems onEarth, and it is important that new technology does notdestroy the environment. Humans must think of both thepositive and negative effects of their inventions.

How can technology affect the environment?When the effects of technology are known, the benefits of

the technology often are more important than the negativeeffects. For example, gasoline-powered cars give people safe, reliable transportation. The negative effects are the environmental problems created by the use of cars.

6. Identify three things thefederal government pays todevelop.

7. Conclude Why is it important for humans tothink about the positiveand negative effects whenthey create technology?


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1. Write a sentence describing one value or belief of your society.

2. Complete the outline to help you organize what you learned about technology.

I. Technology

A. objects

B. Technological or techniques

C. Technological knowledge or

D. systems

II. Global Technological Needs

A. Needs of developing

B. Industrialized countries

C. Differences in nations

D. Bioengineering and supply

3. Complete the table below to help you organize the information you learned about forcesthat shape technology.

society: a group of people that share similar values and beliefs technology: application of scientific knowledge to benefit

people


Government

Private Foundations

Private Companies

Consumers

Citizens

Force How It Shapes Technology

End of

Section


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78 CHAPTER 5 Thermal Energy

There is an old joke that says a sweater is something you puton when your mother is cold. On the lines below, write abouta time when you felt warm, but someone else felt cold.

Before You Read

Read to LearnConduction

The three ways that thermal energy can be transferred fromplace to place are conduction, convection, and radiation.In conduction, heat is transferred by direct contact.Conduction occurs when the particles within a substance orbetween two substances bump into each other and transferkinetic energy. Conduction occurs because the particles inmatter are in constant motion.

How does conduction transfer thermal energy?The figure shows how thermal energy

is transferred when one end of a metalspoon is heated by a flame. The kineticenergy of the particles near the flameincreases. The heated particles bumpinto surrounding particles. In thesecollisions, thermal energy is trans-ferred from particles with more kineticenergy to particles with less kineticenergy. The collisions continue as thermal energy is transferredto the other end of the spoon. When heat is transferred by con-duction, thermal energy is transferred from place to place with-out transferring matter. Thermal energy is transferred by thecollisions between particles, not by movement of matter.

chapter Thermal Energy

section ● Conduction, Convection, and Radiation

5

2

Identify Definitions Asyou read the section, highlightthe definition of each word thatappears in bold.

●B Compare and ContrastMake the Foldable shown belowto help you understand how conduction, convection, and radiation are similar and different.

Conduction

Radiation

Convection

What You’ll Learn

■ the three ways heat istransferred

■ the difference between insulators and conductors

■ how insulators controlthe transfer of thermalenergy


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What are thermal conductors?Energy can be transferred by conduction in all materials.

But energy moves more quickly in some materials than inothers. Conduction is faster in solids and liquids than in gases.In gases, particles are farther apart. Collisions with otherparticles happen less often in gases than in solids or liquids.

The best thermal conductors are metals. Remember that anatom has a nucleus surrounded by electrons. In metals, thereare electrons that are not bound to individual atoms. Theymove easily through the metal and bump into other electrons.This helps the electrons transfer thermal energy. Silver, copper,and aluminum are some of the best energy conductors.

ConvectionThermal energy can also be transferred by a method called

convection. Convection is the transfer of thermal energy in afluid by the movement of warmer and cooler fluids from oneplace to another. A fluid is a substance that can flow. It can be aliquid or a gas. The movement of fluids from one place toanother causes currents. These currents transfer thermal energy.

How is heat transferred by convection currents?When a pot of water is heated on a stove, heat is transferred

by convection currents. First, the water molecules at the bot-tom of the pot gain thermal energy from the stove. The waterbecomes less dense as it is heated. The water at the top of thepot is still cool, so it is more dense than the warm water. Sincethe warm water is less dense, it rises. As it rises, it is replacedat the bottom of the pot by the sinking, cooler water. Thecycle continues until all the water in the pot is at the sametemperature. This rising-and-sinking action is a convectioncurrent. Also, as the warmer water rises, it heats some of thecooler water that it comes in contact with by conduction. In aconvection current, both conduction and convection transferthermal energy.

How do convection and conduction differ?Both convection and conduction transfer heat. However,

convection is different from conduction. Convection transfersthermal energy by moving particles from one place toanother. Warm particles change places with cooler particles.In conduction, thermal energy is transferred by particlesbumping into surrounding particles. But, in conduction,no particles actually move from place to place as they do inconvection.

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1. Explain why metals aregood conductors.

2. Explain A convection oven has a fan to move the air inside it. Is the air in a regular oven alsoaffected by convection?Why or why not?

●C Compare Make the following Foldables to compareconductors and insulators.

Conductors: Insulators:


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RadiationHow does heat travel

through space? There isalmost no matterbetween the Sun andEarth. So heat does nottravel by conduction orconvection. Instead, heatis transferred from theSun to Earth by radiation.

Radiation is the trans-fer of energy by electro-magnetic waves. Theycarry energy throughsolids, liquids, and gases.But they can also carryenergy through emptyspace. Energy transferredby radiation is oftencalled radiant energy.When you sit by a fire-place, you feel warm because heat is transferred by radiationfrom the fire to your skin.

How do radiant energy and matter interact?When radiation strikes a material, three things can happen.

The material absorbs some of the energy. It also reflects some of the energy. And some of the energy may be transmitted, orpassed through, the material. The amount of energy absorbed,reflected, and transmitted depends on the type of material.Light-colored materials reflect more radiant energy, while dark-colored materials absorb more radiant energy. When mate-rial absorbs radiant energy, the thermal energy of the materialincreases. The figure above shows what happens to radiantenergy from the Sun as it reaches Earth.

How is radiation different in solids, liquids, and gases?

Radiant energy can travel through the space between particlesin a solid, liquid, or gas. Particles can absorb the radiation andemit some of the energy they absorbed. This energy then travelsthrough the space between particles. It is absorbed and emittedby other particles. The transfer of energy by radiation worksbest with gases. The particles in gases are much farther apartthan in solids or liquids. This extra space allows the radiantenergy to travel more easily through gases.

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3. Make a Drawing In the first box, draw an ice-covered mountain. Thendraw arrows to show howradiation is reflected andabsorbed by an ice-coveredmountain range. In the second box, draw trees torepresent a rain forest. Then draw arrows to showhow radiation is reflectedand absorbed by a dark rain forest.

Picture This

Outer space

Radiation

Absorbed byatmosphere

Atmosphere

Sun

Reflectedby surface

Reflected byatmosphereReflected byatmosphere

Reflectedby surface

Absorbed byEarth


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Controlling Heat FlowYou probably do things every day to control the flow of heat.

For example, you put on a jacket when you leave your house ona cool morning. And you might wear an oven mitt on yourhand when you reach into the oven to pull out a hot pan. Inboth cases, you use different materials to help control the flow ofheat. Your jacket reduces the flow of heat from your body to thesurrounding air. The oven mitt reduces the flow of heat fromthe hot dish to your hand.

Animal Adaptations Almost all living things have specialfeatures that help them control the flow of heat. The antarcticfur seal has a coat that is about 10 cm thick. This coat helpskeep the seal from losing heat. The emperor penguin has athick layer of blubber and thick, closely spaced feathers. Thishelps the penguin reduce the loss of body heat. These adapta-tions help the animals survive in a climate where the tempera-ture is often below freezing. The scaly skin of the desert spinylizard has the opposite effect. The lizard’s skin reflects the Sun’srays and keeps the lizard from becoming too hot. The leatheryskin also prevents water loss. An animal’s color also can alsohelp it keep warm or cool. The black feathers on a penguin’sback allow it to absorb radiant energy.

Thermal InsulatorsWhen you cook, you want the pan to conduct heat easily

from the stove to your food. But you don’t want the heat tomove easily to the handle of the pan. Most pans have handlesthat are made from insulators. A thermal insulator is a materialin which heat flows slowly. Materials that are insulators includewood, some plastics, fiberglass, and air. An insulator is the oppo-site of a conductor. Remember, conductors are materialsthrough which heat flows quickly. Metals like silver, copper, andaluminum are excellent conductors. Materials that are goodinsulators are poor conductors of heat. That is why many panhandles are made of wood or plastic.

Air as an Insulator Gases, such as air, are usually betterinsulators than solids or liquids. Some types of insulatorscontain many pockets of trapped air. These air pockets con-duct heat poorly and keep convection currents from forming.When you wear a fleece jacket, the fibers in the fleece trap airbetween the jacket and your body. This air slows down theflow of your body heat to the colder air outside the jacket.Your body heat warms the air trapped by the fleece and youare wrapped in a blanket of warm air.

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4. Describe How do animals’colors help them controltheir temperature?

5. Draw Conclusions Some ofthe best cooking pans aremade of copper. Why doyou think this is?


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How are buildings insulated?Materials that are insulators help keep warm air from flow-

ing out of buildings in cold weather. They also keep warm airfrom flowing into buildings in warm weather. These materialsare called insulation. Building insulation is usually made ofmaterials, such as fiberglass or foam, which contain pocketsof trapped air. Insulation is placed between a building’s outerwalls and inner walls and between the ceiling and the attic.It reduces the flow of heat between the building and thesurrounding air.

Insulation also helps furnaces and air conditioners workmore effectively. Since the heat doesn’t escape or enter thebuilding as easily, the furnaces and air conditioners do nothave to work as much. This can save a great deal of energy.In the United States, about 50 percent of the energy used inhomes is used for heating and cooling.

How does a thermos work?Have you used a thermos

bottle like the one in the figure?A thermos bottle lets you keepsoup hot or iced tea cold. It doesthis by reducing the flow ofenergy into and out of the liquidin the bottle. The temperature ofthe liquid hardly changes over anumber of hours. A thermosbottle has two glass walls. Theair between the two walls isremoved so there is a vacuum between the glass layers. Thevacuum contains little matter. This vacuum prevents heattransfer by conduction or convection between the liquid andthe air outside the thermos bottle.

The inside and outside glass surface of a thermos bottle iscoated with aluminum. The coating makes each surfacehighly reflective. Electromagnetic waves are reflected at eachsurface. The inner reflective surface prevents radiation fromtransferring heat out of the liquid. The outer reflective surfaceprevents radiation from transferring heat into the liquid.

Think about the things you do to stay warm or cool. Sittingin the shade reduces the heat transferred to you by radiation.Opening or closing windows increases or reduces heat trans-ferred by convection. Putting on a jacket reduces the heattransferred from your body by conduction. In what otherways do you control the flow of heat?

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Vacuum

Reflectivesurface

Outercase

6. Identify What doesbuilding material insu-lation contain?

7. Explain How does the shinysurface of a thermos bottleprevent heat transfer?

Picture This


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1. Review the terms and their definitions in the Mini Glossary. Write a sentence on the linesbelow that shows your understanding of the term thermal insulator.

2. Complete the table to organize information about how heat is transferred.

3. Think about what you have learned. How did identifying definitions helpyou as you read the section?

Chapter 6

conduction: the transfer of thermal energy by collisions

between particles in matter

convection: when thermal energy is transferred in a fluid by the

movement of warmer and cooler fluid from place to place

radiation: the transfer of energy by electromagnetic waves

thermal insulator: a material in which thermal energy

flows slowly


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Conduction

Convection

Radiation

How Heat Is Transferred Definition Example

End of

Section


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chapter Energy Sources and the Environment

section ● Environmental Impacts

8

4

Create a Quiz As you read thetext, write a quiz question foreach topic. When you havefinished reading, try to answeryour questions correctly.

●D Think Critically Make a 3-tab Foldable. Take notes onhuman impacts to land, water,and air.

Land Water Air

Study Coach

What You’ll Learn■ the causes and effects

of pollution on land,water, and air

■ methods used tocontrol the types andsources of pollution

■ how to protect andpreserve naturalresources

Read to Learn

Before You ReadHow do you think the total number of people on Earth in1900 compares to the human population in 2000? How willthe population change in the next 100 years?

Population and Carrying CapacityHumans share Earth with many other living things. There

are large and small animals. Plants also share Earth. Bears,ants, fish, and trees are examples of populations. Apopulation is the total number of individuals of one speciesoccupying the same area. That area can be large or small. Ahuman population can be of one community, such as LosAngeles, or the entire planet.

Is Earth’s population increasing?In 2000, there were 6.1 billion humans on Earth. Each

day, approximately 200,000 more humans are born. Earth isexperiencing a population explosion. The word explosion isused because the rate at which the population is growing israpidly increasing.

The growth rate of the human population is shown in thegraph on the next page. Notice the slow population growththrough the 1800s. After the mid-1800s, the populationincreased much faster. By 2050, the population is predictedto be about 9 billion—one and a half times what it is now.

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124_151_Ch08_RE_896315.qxd 3/26/10 1:16 AM Page 143 S-034 113:GO00492:GPS_Reading_Essentials_SE%0:XXXXXXXXXXXXX_SE:Application_Files_

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144 CHAPTER 8 Energy Sources and the Environment

What are population limits?Each person uses space and resources. Population size

depends on the amount of resources that are available onEarth and how the population uses those resources. Apopulation without resources will suffer and the populationsize could decrease.

Humans once thought that Earth had an endless supply ofnatural resources, such as fossil fuels, clean water, rich soils,and metals. It’s now known that Earth’s resources are limited.The planet has a carrying capacity. Carrying capacity is thelargest number of individuals of a particular species thatthe environment can support. Unless Earth’s resources aretreated with care, they could disappear and humans couldreach their carrying capacity.

People and the EnvironmentHow will you affect the environment over your lifetime?

By the time you’re 75 years old, you will have producedenough garbage to equal the mass of 11 African elephants—53,000 kg. You will have consumed 18 million liters of water.That’s enough water to fill 68,000 bathtubs. If you live inthe United States, you will have used several times as muchenergy as a person living elsewhere in the world.

How do daily activities affect theenvironment?

Every day, the environment is affected by human activity.The energy for electricity often comes from fossil fuels.Fossil fuels must be mined and then burned to createenergy. Each of these steps changes the environment.

Water that is used must be treated to make it as clean aspossible before being returned to the environment. You eatfood, which needs soil to grow. Many vegetables are grownusing chemical substances, such as pesticides to kill insectsand herbicides to kill weeds. These chemicals can get intowater supplies. If the concentration of chemicals is toogreat, it can threaten the health of living things.

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1. Define What is carryingcapacity?

2. Identify Why are pesticidesand herbicides used whengrowing vegetables?


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What are pollutants?Many of the products humans use are made of plastic and

paper. Plastic is made from oil. The process of refining oil canproduce pollutants, which are substances that contaminatethe environment. Several of the steps used in making papercan damage the environment. Trees are cut down. Trucksuse oil to transport trees to the paper mill. Water and airpollutants are given off in the papermaking process.

Land UsageLand is not often thought of as a natural resource. Yet it

is as important to humans as clean air, clean water, and oil.Land is used for agriculture, logging, garbage disposal, andbuilding. These activities can affect Earth’s land resources.

How does agriculture affect the land?About 16 million km2 of Earth’s total land surface is used

for farming. To feed a growing population, more food needsto be produced. Farmers use chemical fertilizers to increasethe amount of food grown on each km2 of land. Herbicidesand pesticides are also used to reduce weeds, insects, andother pests that can damage crops.

Organic farming techniques include the use of naturalfertilizers, crop rotation, and biological pest controls. Thesemethods help crops grow without using chemicals. However,organic farming cannot currently produce enough food tofeed all of the humans on Earth.

When farmland is tilled, soil is exposed. Without plantroots to hold soil in place, the soil can be carried away byrunning water and wind. Several centimeters of topsoil maybe lost in one year. In some places, it takes more than1,000 years for new topsoil to develop.

How can soil erosion be reduced?Some farmers till, or plow under, the soil before planting

a new crop. Other farmers practice no-till farming andplant seeds between the stubble of last year's vegetationinstead of tilling. Another method is contour plowing. Rowsare tilled across hills and valleys so that runoff from raintraps soil in the plowed rows, reducing soil erosion. Othertechniques include planting vegetation between rows to stopwind erosion. Also a cover crop that is not harvested may beplanted in the off season. These can add nutrients back tothe soil when plowed under.

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3. Summarize What is onemethod used in farming toreduce soil loss?


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What are forest resources?According to the Food and Agriculture Organization of

the United Nations, about one-fourth of the land on Earthis covered by forest. About 55 percent of this forest is foundin developing countries. The other 45 percent occurs indeveloped countries.

Deforestation is the clearing of forested land foragriculture, grazing, development, or logging. It is estimatedthat the amount of forested land in the world decreased by0.24% (94,000 km2) each year between 1990 and 2000. Mostof this deforestation occurred in tropical regions.

Deforestation is a serious concern for many people. Manyplants and animals that live in tropical rain forests cannotsurvive in other places. If their homes are destroyed, theymay become extinct. Many of these plants might beimportant for developing new medicines. Scientists currentlyare researching how deforestation affects plants and animals.

Cutting trees can affect climate as well. Water from treeleaves evaporates into the atmosphere where it can condenseto form rain. If many trees are cut down, less water entersthe atmosphere and that region receives less rainfall. This isone way humans can affect the water cycle.

How does development affect land?Between 1990 and 2000, the number of kilometers of

roadways in the United States increased by more than13 percent. Building highways often leads to more paving asoffice buildings, stores, and parking lots are constructed.

Paving land prevents water from soaking into the soil.Instead, it runs into sewers and streams. Streams are forcedto move a larger volume of water. If enough rainwater flowsinto streams, it increases stream discharge. Then streamsmay flood.

Many communities get their drinking water fromunderground sources. When land is covered with roads,sidewalks, and parking lots, a reduced amount of rainwatersoaks into the ground to refill underground water supplies.

Some communities and businesses have begun to preserveareas rather than pave them. Land is being set aside forenvironmental protection. Co

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4. Explain How can thecutting of trees affect anarea’s climate?

5. Identify Where do manycommunities get theirdrinking water?


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What are hazardous wastes?Land also is used to dispose of garbage. About 60 percent

of our trash is put into sanitary landfills. Some of the wastesthrown away are dangerous to organisms. Wastes that arepoisonous, cause cancer, or can catch fire are calledhazardous wastes. Hazardous wastes used to be put in land-fills with regular household garbage. In the 1980s new lawsmade it illegal for industries to put hazardous wastes intosanitary landfills. New technologies have since been devel-oped to help recycle hazardous wastes. Now there is lessneed to dispose of them.

Is any land being preserved?Not all land on Earth is being used to store waste or

produce something humans can use. Some land remainsmostly uninhabited by humans. National forestlands,grasslands, and national parks in the United States areprotected from development. The map below shows someareas of the country that are used for national parks andpreserves. Many other countries also set aside land fornatural preserves. As the world population continues togrow, the strain on the environment may worsen. Preservingsome land in its natural state will benefit future generations.

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Olympic N.P.

Mount Rainier N.P.

CraterLake N.P.Lassen Volcanic N.P.

Glacier N.P.

Yellowstone N.P.

Badlands N.P.

Rocky Mountain N.P.

Grand Canyon N.P.

Canyonlands N.P.

Saguaro N.P.Carlsbad Caverns N.P.

Big Bend N.P.

Yosemite N.P.

DeathValleyN.P.

Kings Canyon/Sequoia N.P.

Joshua Tree N.P.

Isle Royale N.P.

Mammoth Cave N.P.

Acadia N.P.

Great SmokyMountains N.P.

Shenandoah N.P.

Everglades N.P.

6. Predict What do you thinkcould happen to the wildlifein national parks if the parkswere not protected fromdevelopment?


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Importance of Clean WaterAll organisms need water. Plants need water to make food

from sunlight. Some animals, such as fish and whales, live inwater. Humans and other land animals cannot live withoutdrinking water.

What happens if water isn’t clean? Polluted water containschemicals and organisms that can cause disease and death inmany living things. Water also can be polluted withsediments, such as silt and clay.

Sediment makes water cloudy, blocking the sunlight thatunderwater plants need to make food. Sediment covers theeggs of organisms that live in the water, preventing themfrom getting the oxygen they need to develop.

Can metals cause water pollution?Many metals, such as mercury, lead, and nickel, can be

poisonous. Lead and mercury in drinking water can harmthe nervous system. Yet these metals are part of many usefulitems, such as paints, stereos, and batteries. Today,environmental laws control the amounts of metals releasedwith wastewater from factories. Because metals remain inthe environment for a long time, metals released many yearsago still are polluting bodies of water today.

Mining also releases metals into water. For example, inthe state of Tennessee, more than 43 percent of all streamsand lakes contain metal from mining activities.

How do oil and gasoline pollute water?When it rains, oil and gasoline run off roads and parking

lots into streams and rivers. These compounds containpollutants that might cause cancer. Gas stations storegasoline in tanks below the ground. If the tanks rust, theycan leak gasoline into nearby soil and groundwater. As littleas one gallon of gasoline can make an entire city’s watersupply unsafe for drinking.

Federal laws passed in 1988 require all new gasolinestorage tanks to have a double layer of steel or fiberglass. Inaddition, all new and old tanks must have equipment todetect spills and must be made of material that will notdevelop holes. These laws help protect soil and groundwater. Co

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7. Describe two ways thatmetals enter bodies ofwater.


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What is sewage?When you flush a toilet or take a shower, the water goes

down a drain. This wastewater, called sewage, containshuman waste, household detergents, and soaps. Humanwaste contains harmful organisms that can make peoplesick. In most cities, sewage treatment facilities purify sewagebefore it enters a body of water.

Causes of Air PollutionCities can be exciting places. They are centers of business,

culture, and entertainment. However, cities also have manycars, buses, and trucks that burn fuel for energy. The brownhaze you sometimes see over a city forms from the exhaustof these vehicles. Air pollution also comes from burning fuelin factories, generating electricity, and burning trash. Dustfrom plowed fields, construction sites, and mines alsocontributes to air pollution.

What is smog?One type of air pollution found in and around cities is

called smog. Major sources of smog include cars, factories,and power plants. A combination of pollutants and naturalconditions lead to the formation of smog.

How does smog form?A hazy blanket of smog that forms with the help of

sunlight is called photochemical smog. When gasoline isburned, nitrogen and carbon compounds are released andpollute the air. The figure below shows how thesecompounds produce smog.

Smog

Ozone and other compounds form smog.

D

Oxygen molecules (O2) in air combine with oxygen atoms to form ozone (O3).

C

In the presence of sunlight, nitrogen compounds release oxygen atoms.

B

Car exhaust contains nitrogen and carbon compounds.

A

Picture This8. Identify Circle the step

where photochemical smugis formed.


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Reducing Air PollutionAir pollutants cross the borders between states and

countries, going wherever the wind carries them. This makesthem difficult to control. For example, burning coal inmidwestern states causes acid rain in the northeasternUnited States and Canada.

What is acid rain?Acids form when sulfur oxides from coal-burning power

plants and nitrogen oxides from cars combine with moisturein the air. When acidic moisture falls to Earth as rain orsnow, it is called acid rain.

How has the United States reducedair pollution?

The United States Congress has passed several laws to protectthe air. One was the Clean Air Act of 1990. It helps to reduceair pollution from cars, power plants, and other industries.The Clean Air Act is summarized in the table below.

Can you help reduce air pollution?The Clean Air Act can work only if we all cooperate.

Cleaning the air takes money, time, and effort. How mightyou help reduce air pollution? You might change yourlifestyle by walking, riding a bike, or using publictransportation to get to a friend’s house instead of askingfor a car ride. You also can set the thermostat in your homelower in the winter and higher in the summer.

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9. Explain Why do states andcountries find air pollutiondifficult to control?

Clean Air Regulations

Urban air manufactured since 1996 must reduce nitrogen All cars

pollution missions by 60 percent and hydrocarbons by oxide em

ent from their 1990 levels.35 perce

Acid rain ioxide emissions had to be reduced bySulfur d

on tons from 1990 levels by the year 2000.14 millio

Airborne ttoxins es must limit the emission of 200 compoundsIndustri

use cancer and birth defects.that cau

Ozone-deppleting es were required to immediately cease productionIndustri

chemicalss y ozone-depleting substances inof many 1996.

10. Predict Look at the charton this page. What mightpeople do to reduce airpollutants even further?

11. Identify two ways you canreduce air pollution.


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End of

Section

Sediment_____________

Oil and gasolineFertilizers

_____________

_____________

Water

Pollution

_____________

1. Review the terms and their definitions in the Mini Glossary above. Then write a sentenceusing one of the terms to show how humans can or should take care of the environment.

2. Complete the concept map to show the types of air pollution.

3. Review the questions you wrote as you read this section. What resourcescould you use to find answers to your questions? Did the questions you wrote help youunderstand the information in this section?

Study Coach

acid rain: acidic moisture, with a pH below 5.6, that falls to

Earth as rain or snow and can damage forests, harm

organisms, and corrode structures

carrying capacity: the largest number of individuals of a

given species that the environment can support.

hazardous waste: wastes that are poisonous, cause cancer,

or can catch fire

photochemical smog: hazy, yellow-brown blanket of

smog found over cities that is formed with the help of

sunlight, contains ozone near Earth’s surface, and can

damage lungs and plants

pollutant: substance that contaminates the environment

population: total number of individuals of one species

occupying the same area


P rinter P DF

002 025 ch01 re 896315.qxd 3/31/10 2:09 pm page 2 s-034 ...€¦ · 2 chapter 1 the nature of...

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